Broadband Mid-infrared Laser Research Articles

Broadband, Continuous-Wave, Mid-Infrared Generation Based on ASE Fiber Source

The research reports broadband, continuous-wave (CW), mid-infrared generation based on an optical parametric oscillator (OPO), pumped by an amplified spontaneous emission (ASE) fiber source. The ASE fiber source has a ytterbium (Yb)-doped fiber master oscillator power amplifier (MOPA) structure. By injecting another fiber laser with high power and a narrow linewidth into the nonlinear crystal, the phase-matching difference frequency generation (DFG) can be realized at a low pumping threshold. It is shown that during the down-conversion of the ASE fiber source, the intracavity DFG can steadily and effectively generate a broadband mid-infrared laser, with a central wavelength of 3713 nm. The bandwidth of the mid-infrared laser is 122 nm. The pump power of 2 W generates a 0.238 W mid-infrared laser with a pump-idler conversion efficiency of 11.6%. It has tremendous application potential in the research of broadband CW mid-infrared lasers.

PtSe2 as a Wideband Saturable Absorber for Passively Q-Switched High-Power Mid-Infrared Fiber Laser

We report a transition metal dichalcogenides-PtSe₂ Q-switched single-mode fiber laser operating at 2783.2 nm with a nearly watt-level average output power. We made a PtSe₂ coated highly reflective gold mirror to serve as a saturable absorber mirror. The modulation depth, saturable intensity and non-saturable loss of our PtSe₂ sample were measured to be 10.2&#x0025;, 0.093 GW/cm² and 37.71&#x0025;, respectively. By incorporating the as-prepared saturable absorber mirror in a single-mode Er^3&#x002B;-doped zirconium fluoride fiber laser, stable Q-switched laser pulses were obtained with a maximum average power of 932.7 mW. The pulse duration and repetition rate were <inline-formula> <tex-math notation="LaTeX">$1.04 ~\mu \text{s}$ </tex-math></inline-formula> and 93.10 kHz, respectively. The corresponding pulse energy was <inline-formula> <tex-math notation="LaTeX">$10.02 ~\mu \text{J}$ </tex-math></inline-formula> and the slope efficiency was 18.1&#x0025;. By employing a plane ruled grating in the resonator, we also investigated the operating wavelength range of the PtSe₂-coated mirror. A continuously wavelength-tunable Q-switched laser was obtained from 2733.0 nm to 2803.0 nm. To the best of our knowledge, this is the first demonstration of PtSe₂ working as a saturable absorber for the 2.73-<inline-formula> <tex-math notation="LaTeX">$2.80 ~\mu \text{m}$ </tex-math></inline-formula> waveband, and the Q-switched laser presents threefold and twofold increase in output power and pulse energy, respectively, over previously reported values achieved from &#x007E;3-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> single-mode Q-switched fiber lasers enabled by two-dimensional materials. The results indicate that PtSe₂ is an excellent wideband optical switch for high-power broadband mid-infrared laser pulses generation.

Structure design and numerical simulation of chirped periodically polarized lithium niobate crystal for broadband mid-infrared laser generation

Mid-infrared band 3–5 &lt;inline-formula&gt;&lt;tex-math id="M1"&gt;\begin{document}${\text{μm}}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20220016_M1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20220016_M1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; laser light source has important applications in many fields such as medical treatment, basic science, communication, and industry. Owing to the limitation to available efficient gain media in the mid-infrared band, the traditional methods of generating and amplifying lasers , such as regenerative amplification, are no longer applicable. In order to produce broadband and high-energy mid-infrared laser, in this work we combine quasi-phase matching technology and chirped periodically polarized lithium niobate (CPPLN) crystal for theoretical analysis and numerical design. The second-order nonlinear difference-frequency generation (DFG) process is used to implement the generation of mid-infrared laser via CPPLN. In the differential frequency process, the pump light used is 800 nm in wavelength and the wavelength range of signal light is 0.95–1.6 &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}${\text{μm}}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20220016_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20220016_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. By calculating the dispersion curve of CPPLN crystal, the phase mismatch of difference frequency generation processes with different light signals is obtained. Under the condition of quasi-phase matching, the CPPLN with deliberately poling structures is designed and used to provide phase mismatch compensation in a broad bandwidth. The designed structure can meet the generation of mid infrared laser in a 1.6–5&lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}$ {\text{μm}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20220016_M3.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20220016_M3.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; band according to the numerical simulations. The conversion efficiencies of mid-infrared laser with different wavelengths at different positions in the crystal are obtained by using nonlinear coupled wave equations and fourth-order Runge-Kutta method. The results show that the mid-infrared laser in a wavelength range of 1.6–5 &lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}$ {\text{μm}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20220016_M4.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20220016_M4.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; can be produced efficiently in a single CPPLN crystal, with an average conversion efficiency of about 15%. The theoretical analysis and numerical simulation for the designed CPPLN crystal can provide good schematic reference and theoretical support for further experimental exploration on generation of mid-infrared laser.

啁啾脉冲光学参量振荡器及宽谱中红外激光的产生（特邀）

啁啾脉冲光学参量振荡器及宽谱中红外激光的产生（特邀）

Investigation of broadband mid-infrared emission and quantitative analysis of Dy-Er energy transfer in tellurite glasses under different excitations

Broadband mid-infrared emissions are obtained from Dy3+/Er3+ co-doped tellurite glasses under 808 or 980 nm excitation. The maximum effective emission bandwidths of mid-infrared emission is 92.45 nm in Dy3+/Er3+ co-doped tellurite glass pumped by 808 nm, while it can reach 209.00 nm pumped by 980 nm. The effects of different laser excitations on the energy transfer mechanism between Dy3+ and Er3+ ions have been investigated in tellurite glasses. Under 808 nm excitation, the energy transfer efficiency from Er3+:4I13/2 to Dy3+:6H11/2 level is 73.1% and the energy transfer coefficient from Er3+:4I11/2 to Dy3+:6H5/2 level and from Er3+:4I13/2 to Dy3+:6H11/2 level are 6.89 × 10−38 and 0.01 × 10−38 cm6/s, respectively. Under 980 nm excitation, the energy transfer efficiency from Er3+:4I13/2 to Dy3+:6H11/2 level can reach as high as 80%. Moreover, the maximum emission cross-section of 2500-3100 nm broadband emission when pumped by 808 nm is 1.90 × 1020 cm2 at 2765 nm, while it can reach as high as 4.99 × 1020 cm2 at 2724 nm pumped by 980 nm. Thus, the 980 nm excitation is more efficient for Dy3+/Er3+ co-doped tellurite glass to realize low-threshold and high gain applications at broadband mid-infrared laser.

Progress in monolithic, broadband, widely tunable midinfrared quantum cascade lasers

We present recent progress on the development of monolithic, broadband, widely tunable midinfrared quantum cascade lasers. First, we show a broadband midinfrared laser gain realized by a heterogeneous quantum cascade laser based on a strain balanced composite well design of Al0.63In0.37As/Ga0.35In0.65As/Ga0.47In0.53As. Single mode emission between 5.9 and 10.9 μm under pulsed mode operation was realized from a distributed feedback laser array, which exhibited a flat current threshold across the spectral range. Using the broadband wafer, a monolithic tuning between 6.2 and 9.1 μm was demonstrated from a beam combined sampled grating distributed feedback laser array. The tunable laser was utilized for a fast sensing of methane under pulsed operation. Transmission spectra were obtained without any moving parts, which showed excellent agreement to a standard measurement made by a Fourier transform infrared spectrometer.

Active intensity noise suppression for a broadband mid-infrared laser source.

Excess relative intensity noise (RIN) constitutes one of the major limitations of most spectroscopic methods involving lasers. Here, we present an active RIN suppression scheme for a coherent mid-infrared (MIR) light source (8.4-11 µm), based on intra-pulse difference frequency generation (DFG). Three different stabilization concepts that rely on modulating the intensity of the driving near-infrared (NIR) pulse train with an acousto-optic modulator are investigated and compared. By using the wings of the NIR spectrum to generate the error signal, a RIN suppression of the MIR pulse train of up to a factor of 20 was achieved in the band between 1 Hz and 100 kHz, resulting in a total integrated RIN of 0.07%.

Fiber laser-pumped, chirped, PPMgLN-based high efficient broadband mid-IR generation

We demonstrate a high-efficiency, high-power-nanosecond fiber laser-pumped broadband mid-infrared output based on a linearly chirped PPMgLN crystal. By using a linearly polarized pulsed Yb-doped fiber laser as the pump, we experimentally obtain a 1.22-W broadband mid-infrared laser output under pump power of 10.15 W. The 3-dB bandwidths of the idler and signal output are approxiwately 150 and 13 nm, centering at 3.60 and 1.51 ?m, respectively. The measured idler spectrum shows a smooth spectral profile.

Mid-infrared upconversion spectroscopy based on a Yb:fiber femtosecond laser

We present a system for molecular spectroscopy using a broadband mid-infrared laser with near-infrared detection. Difference frequency generation of a Yb:fiber femtosecond laser produced a mid-infrared (MIR) source tunable from 2100–3700 cm−1 (2.7–4.7 µm) with average power up to 40 mW. The MIR spectrum was upconverted to near-infrared wavelengths for broadband detection using a two-dimensional dispersion imaging technique. Absorption measurements were performed over bandwidths of 240 cm−1 (7.2 THz) with 0.048 cm−1 (1.4 GHz) resolution, and absolute frequency scale uncertainty was better than 0.005 cm−1 (150 MHz). The minimum detectable absorption coefficient per spectral element was determined to be 4.4×10−7 cm−1 from measurements in low pressure CH4, leading to a projected detection limit of 2 parts-per-billion of methane in pure nitrogen. In a natural atmospheric sample, the methane detection limit was found to be 30 parts-per-billion. The spectral range, resolution, and frequency accuracy of this system show promise for determination of trace concentrations in gas mixtures containing both narrow and broad overlapping spectral features, and we demonstrate this in measurements of air and solvent samples.

High-power broadband laser source tunable from 30 μm to 44 μmbased on a femtosecond Yb:fiber oscillator

We describe a tunable broadband mid-infrared laser source based on difference-frequency mixing of a 100 MHz femtosecond Yb:fiber laser oscillator and a Raman-shifted soliton generated with the same laser. The resulting light is tunable over 3.0 um to 4.4 um, with a FWHM bandwidth of 170 nm and maximum average output power up to 125 mW. The noise and coherence properties of this source are also investigated and described.

A broadband mid-infrared laser magnetic resonance spectrometer for the spectral range of 1200?2000 wavenumbers

A broadband mid-infrared laser magnetic resonance spectrometer is described, which can be operated in intracavity or extracavity configuration. The specially designed CO-laser gain tube allows operation from 1220–2000 cm−1. Experimental details and examples of spectroscopic applications are discussed.